1. Field of the Invention
The present invention relates to a method, system, and program for estimating coil resistance of a Voice Coil Motor (VCM) in a disk drive system.
2. Description of the Related Art
Computer hard disk drives include one or more disks of magnetic storage medium and a disk drive head assembly to read and write data on the magnetic storage medium. Magnoresistive (MR) heads typically include a write element comprised of a thin film inductive head and a read element comprised of a sensor. MR heads for the disk surfaces of the disk drive are affixed to an actuator or arm that glides across the disk surface to position the head at different track locations. Current is passed to a voice coil motor (VCM) to position the actuator with respect to the disk surface. The amount of torque applied to the actuator is governed by the amount of current in the VCM. The VCM comprises the coil that receives the current and two magnets. During operations, the disk drive components, such as the VCM, can produce vibrations induced as a result of the resonance of the components. Such vibrations may result in undesirable head variations and tracking errors.
One factor leading to an increase demand in attenuating vibrations and noise produced by the VCM is the increased demand for higher storage capacity and faster Input/Output (I/O) access in disk drives. High disk operation speeds require higher voltages to generate more current to the VCM so that sufficient torque is created to actuate movement of the actuator (head-arm) assembly at the higher speeds. Higher voltages subjects the VCM to greater acoustic and mechanical energy, which may result in increased noise and vibrational problems.
In current disk drive systems, to correct for tracking errors resulting from noise and vibrations from components such as the VCM, the disk drive controller will read servo information indicating the actual current position and compare that value read to the desired position. The drive controller will then calculate a current to apply to the VCM to correct any variation in the measured position versus desired position. Thus, the current supplied to the VCM to apply torque to the actuator arm is a function both of the amount of current in the voice coil supplied by an amplifier controlled by the drive controller and by position feedback adjustments based on position information read from the data heads.
Other techniques to reduce VCM vibrational noise includes the use of lighter and stiffer suspension elements in the actuator that have much higher natural frequencies. Also smaller and lighter slider designs provide less contact areas for the transmission of vibrations and noise from the VCM. However, there are design constraints on further reductions in size of the actuator to reduce vibrations and noise. Another solution to alleviate noise is to use suspension dampers to dissipate energy transmitted through the actuator and reduce the amount of vibrations and noise produced by the VCM.
Notwithstanding the current efforts to reduce the vibrations and noise produced by the VCM, there is a continued need in the art to attenuate the effect of vibrations and noise emanating from the VCM on disk drive performance.